12 The First Lines of Morphology 
have supposed is from the former to the latter. But it so 
happens, in the actual circumstances of our world, that there 
are many alternations both ways, and always one, at least, in 
the course of every day. We have therefore still to investi- 
gate, and if possible to determine, that form which shall be 
the most successful compromise between both—which shall be 
most safe during unfavourable vicissitudes, and most open to 
take advantage of every favourable change. Now, such a 
form we obviously obtain, when the solid sphere, the form of 
hybernation, (1) in opening into a membrane as the form of 
development, does so in such a way as to issue in a hollow 
spherical membrane pervious to the ambient medium, or (2) 
when extending into a filament it turns round upon itself as 
a helix, and thus generates a hollow spherical form by a spiral 
filament. Thus, as the perfected or matured form of an ele- 
mentary orgasm, we reach 
a simple membrane, 
The Spherical Cell, its cell watt ho both. 
a spiral filament, 
Moreover, it follows, from our principle, that when the con- 
dition of existence is favourable to life, this spherical cell 
must tend to grow and increase to the utmost limits of size 
which it can without falling to pieces; for it must tend to be- 
come more and more pervious and fenestrated, so as to place 
its interior as much as possible in a condition as favourable as 
its exterior, with respect to the ambient medium. But when 
the relations of the ambient medium change, and become unfa- 
vourable, then it must tend to diminish the extent of surface 
exposed to that medium; it must tend to contract; whereby 
not only will the extent of the external surface be lessened, 
and that surface so far secured from injury, but the fenestre, 
pores or mouths, also, may possibly be closed, and thus the 
ambient medium excluded from the interior altogether. 
Thus, as the most perfect and mature organic element 
which our method enables us to reach, we obtain a pervious 
spherical cell capable of growth, and of expanding or con- 
tracting according as the conditions of existence are favour- 
able or unfavourable to the deployment of life. Now, in 
reference to this result, still more than in reference to the two 
which have preceded, it is surely unnecessary to enlarge by 
